Aberrant glycosylation accompanies some of the other mutations commonly observed in carcinomas. It has been estimated that about 80% of all carcinomas express a truncated glycan, the Tn Antigen. With few exceptions Tn and the sialylated form Sialyl Tn (STn), are not expressed in normal, healthy tissues. Furthermore, the non-human immunogenic sialic acid, N-glycolylneuraminic acid (Neu5Gc), seems to be differentially expressed on carcinomas such as breast cancer in the form of Neu5Gc-STn (GcSTn).
Multiple aberrant glycosylation forms have been described in human cancers, identifying specific glycans as a class of cell surface molecules suitable for specific tumor targeting (Cheever, M. A. et al., The prioritization of cancer antigens: a national cancer institute pilot project for the acceleration of translational research. Clin Cancer Res. 2009 Sep. 1; 15(17):5323-37). For example, various human cancer types (such as bladder, breast, cervical, colon, lung, and ovarian cancer among others) show high expression of STn antigen, which is rare in normal human tissues (Karlen, P. et al., Sialyl-Tn antigen as a marker of colon cancer risk in ulcerative colitis: relation to dysplasia and DNA aneuploidy. Gastroenterology. 1998 December; 115(6):1395-404; Ohno, S. et al, Expression of Tn and sialyl-Tn antigens in endometrial cancer: its relationship with tumor-produced cyclooxygenase-2, tumor-infiltrated lymphocytes and patient prognosis. Anticancer Res. 2006 November-December; 26(6A):4047-53). In addition, the presence of STn on tumor-associated mucins relates to cancer with poor prognosis and is therewith considered an attractive epitope for cancer detection and targeted therapy (Cao, Y. et al., Immunodetection of epithelial mucin (MUC1, MUC3) and mucin-associated glycotopes (TF, Tn, and sialosyl-Tn) in benign and malignant lesions of colonic epithelium: apolar localization corresponds to malignant transformation. Virchows Arch. 1997 September; 431(3):159-66; Julien, S. et al., Sialyl-Tn vaccine induces antibody-mediated tumour protection in a relevant murine model. Br J. Cancer. 2009 Jun. 2; 100(11):1746-54; Itzkowitz, S. H. et al., Sialosyl-Tn. A novel mucin antigen associated with prognosis in colorectal cancer patients. Cancer. 1990 Nov. 1; 66(9):1960-6; Motoo, Y. et al., Serum sialyl-Tn antigen levels in patients with digestive cancers. Oncology. 1991; 48(4):321-6; Kobayashi, H. et al., Serum sialyl Tn as an independent predictor of poor prognosis in patients with epithelial ovarian cancer. J Clin Oncol. 1992 January; 10(1):95-101). Tn and STn formation is associated with somatic mutations in the gene Cosmc that encodes a molecular chaperon required for the formation of the activate T-synthase (Ju, T. et al., Protein glycosylation: chaperone mutation in Tn syndrome. Nature. 2005 Oct. 27; 437(7063):1252; Ju, T. et al., Human tumor antigens Tn and sialyl Tn arise from mutations in Cosmc. Cancer Res. 2008 Mar. 15; 68(6):1636-46). It can also result from increased expression of the sialyl transferase, ST6GalNAc-I (Ikehara, Y. et al., Cloning and expression of a human gene encoding an N-acetylgalactosamine-alpha-2,6-sialyltransferase (ST6GalNAc I): a candidate for synthesis of cancer-associated sialyl-Tn antigens. Glycobiology. 1999 November; 9(11):1213-24; Brockhausen, I. et al., Pathways of mucin O-glycosylation in normal and malignant rat colonic epithelial cells reveal a mechanism for cancer-associated Sialyl-Tn antigen expression. Biol. Chem. 2001 February; 382(2):219-32). De-novo expression of STn can modulate carcinoma cells, change the malignant phenotype, and lead to more aggressive cell behaviors (Pinho, S. et al., Biological significance of cancer-associated sialyl-Tn antigen: modulation of malignant phenotype in gastric carcinoma cells. Cancer Lett. 2007 May 8; 249(2):157-70). Although STn is highly expressed in malignant tissues, low levels are also found on healthy human cells (Jass, J. R. et al., Distribution of sialosyl Tn and Tn antigens within normal and malignant colorectal epithelium. J. Pathol. 1995 June; 176(2):143-9; Kirkeby, S. et al., MUC1 and the simple mucin-type antigens: Tn and Sialyl-Tn are differently expressed in salivary gland acini and ducts from the submandibular gland, the vestibular folds, and the soft palate. Arch Oral Biol. 2010 November; 55(11):830-41). STn alone has attracted attention as a target for cancer detection and therapy (Cheever, M. A. et al., The prioritization of cancer antigens: a national cancer institute pilot project for the acceleration of translational research. Clin Cancer Res. 2009 Sep. 1; 15(17):5323-37).
In addition to the presence of STn, other glycosylation changes have been described in cancer. One of them involves Neu5Gc. N-acetylneuraminic acid (Neu5Ac) and Neu5Gc are the two major sialic acids on mammalian cell surfaces. Neu5Ac and Neu5Gc differ only in that Neu5Gc comprises an additional oxygen atom associated with chemical group attached to carbon 5. Due to the loss of a functional gene, humans can only synthesize sialic acid in the form of Neu5Ac, but not Neu5Gc. However Neu5Gc can be metabolically incorporated into humans from animal-derived dietary sources such as red meats (Tangvoranuntakul, P. et al., Human uptake and incorporation of an immunogenic nonhuman dietary sialic acid. Proc Natl Acad Sci USA. 2003 Oct. 14; 100(21):12045-50; Nguyen, D. H. et al., Effects of natural human antibodies against a nonhuman sialic acid that metabolically incorporates into activated and malignant immune cells. J. Immunol. 2005 Jul. 1; 175(1):228-36; U.S. Pat. Nos. 7,682,794, 8,084,219, US2012/0142903, WO2010030666 and WO2010030666, herein incorporated by reference in their entirety). Neu5Gc is significantly abundant among human tumors (Higashi, H. et al., Characterization of N-glycolylneuraminic acid-containing gangliosides as tumor-associated Hanganutziu-Deicher antigen in human colon cancer. Cancer Res. 1985 August; 45(8):3796-802; Miyoshi I. et al., Detection of 4-O-acetyl-N-glycolylneuraminyl lactosylceramide as one of tumor-associated antigens in human colon cancer tissues by specific antibody. Mol. Immunol. 1986. 23: 631-638; Hirabayashi, Y. et al., Occurrence of tumor-associated ganglioside antigens with Hanganutziu-Deicher antigenic activity on human melanomas. Jpn J Cancer Res. 1987. 78: 614-620; Kawachi. S, et al., Heterophile Hanganutziu-Deicher antigen in ganglioside fractions of human melanoma tissues. Int Arch Allergy Appl Immunol. 1988. 85: 381-383; Devine, P. L. et al., The breast tumor-associated epitope defined by monoclonal antibody 3E1.2 is an O-linked mucin carbohydrate containing N-glycolylneuraminic acid. Cancer Res. 1991. 51: 5826-5836; Malykh, Y. N. et al, N-Glycolylneuraminic acid in human tumours. Biochimie. 2001. 83: 623-634) and remarkably low in normal human tissues, which had been overlooked for several decades (Diaz, S. L. et al., Sensitive and specific detection of the non-human sialic Acid N-glycolylneuraminic acid in human tissues and biotherapeutic products. PLoS One. 2009. 4: e4241; Tangvoranuntakul, P. et al., Human uptake and incorporation of an immunogenic nonhuman dietary sialic acid. Proc Natl Acad Sci USA. 2003. 100: 12045-12050; Varki, A. et al., Multiple changes in sialic acid biology during human evolution. Glycoconj J. 2009. 26: 231-245.) The increased metabolic accumulation of diet-derived Neu5Gc in cancer tissue compared to healthy human tissues is likely explained by at least three factors: rapid growth with underproduction of competing endogenous Neu5Ac, enhanced macropinocytosis induced by growth factors (Dharmawardhane, S. et al., Regulation of macropinocytosis by p21-activated kinase-1. Mol Biol Cell. 2000 October; 11(10):3341-52; Simonsen, A. et al., The role of phosphoinositides in membrane transport. Curr Opin Cell Biol. 2001 August; 13(4):485-92; Johannes, L. et al., Clathrin-dependent or not: is it still the question? Traffic. 2002 July; 3(7):443-51; Amyere, M. et al., Origin, originality, functions, subversions and molecular signaling of macropinocytosis. Int J Med. Microbiol. 2002 February; 291(6-7):487-94), and the upregulation of gene expression of the lysosomal sialic acid transporter gene sialin by hypoxia (Yin, J. et al., Hypoxic culture induces expression of sialin, a sialic acid transporter, and cancer-associated gangliosides containing non-human sialic acid on human cancer cells. Cancer Res. 2006 Mar. 15; 66(6):2937-45). In addition, all humans tested to date comprise a polyclonal antibody reservoir against non-human Neu5Gc, which makes it the first example of a xeno-autoantigen (Padler-Karavani, V. et al., Diversity in specificity, abundance, and composition of anti-Neu5Gc antibodies in normal humans: potential implications for disease. Glycobiology. 2008 October; 18(10):818-30; Varki, N. M. et al., Biomedical differences between human and nonhuman hominids: potential roles for uniquely human aspects of sialic acid biology. Annu Rev Pathol. 2011; 6:365-93). The accumulation of dietary Neu5Gc in malignant tumors in the face of an anti-Neu5Gc response was shown to facilitate tumor progression by inducing a low-grade chronic inflammation (Hedlund, M. et al., Evidence for a human-specific mechanism for diet and antibody-mediated inflammation in carcinoma progression. Proc Natl Acad Sci USA. 2008 Dec. 2; 105(48):18936-41). Thus, Neu5Gc containing glycan epitopes on human tumors represent a valuable possibility for drug targeting. A recent study suggests the existence of antibodies against Neu5Gc-containing STn (GcSTn), but not Neu5Ac-STn (AcSTn), in cancer patients and explores their potential as a specific biomarker for cancer detection (Padler-Karavani, V. et al., Human xeno-autoantibodies against a non-human sialic acid serve as novel serum biomarkers and immunotherapeutics in cancer. Cancer Res. 2011 May 1; 71(9):3352-63).
However, the available antibodies have major drawbacks as they likely do not detect GcSTn and react only AcSTn by definition. There remains a need for antibodies specific for GcSTn. There are important methodological reasons for this gap. First, Neu5Gc is widely present in non-human mammals, and hence mammalian cell lines, which are conventionally utilized for antibody production. Under normal conditions it is difficult to gain immunity against a “self” molecule. Second, the myeloma cells commonly used as fusion partners to establish a hybridoma endogenously produce and expresses Neu5Gc. The endogenous production and expression may cause the binding of this antigen to antibody produced from the same cells. This situation would likely result in poor antibody yield and/or reduced survival of the hybridoma cells. Third, in most cases, the antibody producing cells are cultured in media that contain animal products (such as fetal calf serum), which also prevents the production of antibodies specific against Neu5Gc containing epitopes creating yet another barrier to the production of GcSTn.